This invention relates to tire-reinforcement fabric composed of warp cords of synthetic organic filaments, glass or wire, and weft yarns for maintaining the cords in properly spaced relationship. The invention is more particularly concerned with improvements in the weft yarns.
The use of reinforcing fabric in tires is disclosed in Wolf et al. U.S. Pat. No. 3,395,744. Plies of strong cords are used to reinforce the tire. The purpose of the weft yarns is merely to maintain the cords in spaced relationship during processing of fabric plies and construction of the tire. Cotton weft yarns have been used for bias ply constructions to maintain uniform spacing of the cords, but they are not satisfactory for radial ply constructions.
The carcass of a radial tire is normally assembled on a flat drum and is then expanded to a toroidal shape. Space between cords in the crown of the tire is thereby increased to at least 75 percent over the original value. Cotton weft yarns break at about 12 percent or less elongation and the fabric splits at the breaks to leave gaps, since the weft yarns restrain the warp cords in unbroken weft areas. Proper cord spacing is particularly critical in monoply radial tires. If x-ray observation shows that the cord spacing is not acceptably uniform, the tire must be downgraded or even rejected.
The Wolf et al. patent states that a weft yarn of a form of nylon filaments commonly referred to by the art as unoriented (undrawn) nylon has been found to be particularly successful, and that the weft yarn can consist essentially of other crystalline resins possessing the proper elongation when in an unoriented state. A polyester of the type described in Whinfield and Dickson U.S. Pat. No. 2,465,319 dated Mar. 22, 1949, is mentioned. Such weft yarns have high elongation as produced, but the break elongation quickly drops to less than 50 percent when the weft yarn is exposed to the temperatures of 400.degree.-450.degree. F. (204.degree.-232.degree. C.) used with recent warp cord materials. Furthermore, cotton weft yarns have a substantially higher initial modulus which is desirable to minimize cord distortion during fabric processing steps of coating, calendering and assembling the tire carcass.